In a general dialysis treatment, blood collected from the patient is extracorporeally circulated and is then returned to the body of the patient through a blood circuit. The blood circuit basically includes an arterial blood circuit and a venous blood circuit that are connectable to a dialyzer (a blood purification device) including, for example, hollow fiber membranes. The arterial blood circuit and the venous blood circuit are provided at the distal ends thereof with an arterial puncture needle and a venous puncture needle, respectively, which are stuck into the patient, whereby the blood is extracorporeally circulated during the dialysis treatment.
The arterial blood circuit, which is one of the two blood circuits, is provided with a peristaltic blood pump. When the blood pump is activated with the arterial puncture needle and the venous puncture needle being stuck in the patient, blood collected from the body of the patient can be delivered into the dialyzer while being extracorporeally circulated. Furthermore, an arterial air-trap chamber and a venous air-trap chamber are connected to the arterial blood circuit and the venous blood circuit, respectively. Bubbles contained in the blood that is under extracorporeal circulation are purged (removed) in the air-trap chambers. Then, the resulting blood is returned to the body of the patient.
Known air-trap chambers disclosed by, for example, PTL 1 and PTL 2 are each a chamber having a storing space in which an air layer, a substitution fluid layer (a layer of a physiological saline solution or the like), and a blood layer are formable in that order from the top, so that air in the blood circulating through a blood circuit is removed by being collected in the air layer. That is, the substitution fluid layer interposed between the blood layer and the air layer prevents the blood in the blood layer from directly coming into contact with the air in the air layer. Hence, the coagulation of the blood can be suppressed.
PTL 1: Japanese Registered Utility Model No. 3128724
PTL 2: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-530543